Suspension concentrate or aqueous flowable pesticidal compositions are concentrated suspensions of water insoluble pesticides and mixtures of pesticides in aqueous systems. The present invention relates to stable such pendimethalin compositions.
Pendimethalin is a dinitroaniline that exists in polymorphic form, both in orange crystal form and yellow crystal form. U.S. Pat. Nos. 4,082,537 and 4,150,969 address pendimethalin's unique formulation problems and provide ways to avoid formation and/or presence of the larger, orange crystal form (both incorporated herein by reference). It is believed that the presence of pendimethalin in the orange macrocrystal form results in large elongated crystals in final formulations.
In order to formulate stable wettable powder compositions of pendimethalin, these two patents disclose utilizing a stabilized pendimethalin, stabilized by the addition of either sodium dialkyl (C.sub.6 -C.sub.8) sulfosuccinate or an ethoxylated .beta.-diamine. This technique maintains pendimethalin in the yellow crystal form which does not favor the formation of large elongated crystals in formulated product for the preparation of wettable powders. However, these patents fail to disclose ways to formulate pendimethalin as a stable suspension concentrate composition or aqueous flowable composition with orange crystal forms, which form is favored.
These aqueous compositions frequently contain about 10% to 80%, by weight of a solid pesticide or mixture of solid pesticides, thereby providing a method for handling those pesticides which are relatively water insoluble in an aqueous medium. Since these types of compositions have the desirable characteristics of a thick liquid, they may be poured or pumped. Thus, some of the problems, like dusting that is possible in solid compositions of wettable powders and granulars, are avoided. Further, these aqueous-based concentrates also have the added advantage of not requiring the use of organic solvents, often present in emulsifiable concentrates.
For these reasons, it is desirable to formulate pesticides into suspension concentrates or aqueous flowables. However, such formulations have their own problems such as gelling, caking and settling, as well as problems because of the physical and chemical characteristics of the pesticide or mixture of pesticides. Pendimethalin is one of these pesticides that is somewhat difficult to formulate.
Oftentimes, when pendimethalin in the orange macrocrystal form is found in compositions, very large, elongated crystals (about 3000 microns in length) appear in final product, resulting in instability, difficulty in processing and unreliability of usage. Thus, formulating compositions wherein these elongated crystals do not develop is crucial to stability and necessary to obtain even distribution of active compound for application.
The problems associated with the development of suspension concentrate compositions containing low melting active ingredients, alone or in combination with higher melting active ingredients, are described in German patent application No. DE 3302648 A1. German patent application No. DE 3302648 A1 tries to deal with the problems of an aqueous mixed dispersion of a low melting active ingredient in a solvent of phthalic acid C.sub.1 -C.sub.12 alkyl esters in combination with an aqueous suspension concentrate containing one or more active ingredients as an alternative to a suspension concentrate containing low melting active ingredients, such as pendimethalin[N-(1-ethyl-propyl)-2,6-dinitro-3,4-xylidine]. The reason for the alternative approach of that application is the inability to prepare stable suspension concentrates by various techniques, including those of European patent application 0 33291.2 That EPO application describes insecticidal suspension concentrate compositions of phosalone and adjuvants which may be prepared with molten insecticidie. These references do not address ways helpful to the development of pendimethalin compositions which utilize the orange crystal form to produce a stable and evenly efficacious product.
It is an object of the present invention to provide stable aqueous concentrate compositions of the low melting pesticide, pendimethalin, in the orange crystal form either alone or in combination with secondary pesticide(s) in order to avoid the problem of formation of large elongated crystals of formulated pendimethalin. These secondary pesticides are often water insoluble or have melting points greater than 70.degree. C.
It is a further object of this invention to provide such stable aqueous suspension concentrate compositions of pendimethalin having a ratio of orange crystal to yellow crystal of 4:96 to totally (100%) orange crystal form.
Furthermore, an additional object of the present invention is to provide methods for preparing such stable aqueous suspension concentrate compositions.
These and other objects will become more apparent by the detailed description of the invention provided herein.